Pressure Testing Gas Line

Hi everyone, wondering if anyone had any insight here. I just had some gas line installed by a plumber. When he finished he put air into the line (25PSI). A day later the pressure has dropped to (11PSI). He mentioned it should be anything to worry about because air changed and expands based on temp and he also mentioned that his valve maybe leaking. So my question is does that make much sense? If the PSI is dropping doesn't that mean there is a leak in the system and when gas gets connected isn't it going to leak out as well?

I'm not a plumber, but that smells like BS to me. Air pressure in a confined volume will change with temperature but a 14 PSI drop over one day sounds far too big to be entirely a thermal issue. There's probably a hole somewhere.

Thermal pressure changes go BOTH ways, down when it cools and up when it gets hot, but the air does not "disappear". He has a slight leak, possibly at his gauge, but he should FIND it. He may be counting on the fact that it appears to be a "small" leak, and since the gas will be at 1/100 of the test pressure it MIGHT not leak out, or if it does, it would be in such a small concentration that it would not be dangerous, if it cannot collect in a closed space.